The invention relates to a pipe joint for joining a tubular component to a receiving piece, the pipe joint comprising a fitting body having a recess for receiving the tubular component, a tightening nut having a first thread and a second thread, the fitting body having a first thread corresponding to the first thread of the tightening nut, and a cutting ring between the tightening nut and the fitting body, the cutting ring being arranged to be pressed between a wedge-like wall portion of the recess, and the tubular component when the tightening nut is tightened. The tightness of the joint is based on sealing achieved by the metallic “cutting ring”. In this context, the term receiving piece refers to any point of attachment used in various applications of the pipe joint. For example, the receiving piece can be a wall of a container or a recipient, a pump, a thread of a tubular component, etc.
From DIN standard No. 2353 is known a joint whose tightness is not based on the use of a seal made of rubber material but on the sealing provided by a metallic cutting ring. When the tightening nut is turned towards the fitting body, the cutting ring presses in a wedge-shaped space towards the first tubular component cutting into an outer surface thereof and tightening against it, and at the same time it tightens towards inner surfaces of the tightening nut and the fitting body. The tighter the nut is turned, the closer the cutting ring cuts in the pipe and the joint becomes stronger. The DIN standard defines fittings for pipe diameters of 4 to 42 mm. The pitch of a thread at a first end of the fitting body, i.e. of a first thread, is 1 to 2 mm depending on the pipe size, so that the wider the pipe, the larger the pitch.
To provide the above-described sealing, the tightening nut must be turned with sufficient force. The tightening nut of a large joint must be turned with greater torque than the tightening nut of a small joint.
A problem with the above-described known joints can be that the torque required by the tightening nut is great particularly when large-diameter pipes are concerned. This problem becomes more apparent if the joint is located in a confined space without any room for big tools. Instead, one has to use a small tool that must be wrenched with great force in a confined space so as to achieve a sufficient torque and a firm joint. By using a smaller pitch in a tightening nut/fitting body combination the required torque would be lower, but firstly, fittings of this kind are not available, because the fitting bodies are standardized having relatively large pitches, and secondly, a smaller pitch is technically more difficult to manufacture than a larger pitch. Moreover, a very considerable fact is that a fine and long thread would be slow to mount.